1. Field of the Invention
This invention relates to assay devices and is directed more particularly to methods for using a diagnostic device for conducting enzymatic and chromogenic assays of liquid substances.
2. Description of the Prior Art
Assays are useful for the quantitation of antigen/hapten, antibody analyte, or analyte occurring on or attached to cells, or other particulate material, contained in liquid samples of body fluids, such as serum, plasma, urine, or saliva, and non-body fluids, such as cell culture media, potable water, and waste water.
A known assay device includes a housing having a number of "wells" therein, which serve as reaction vessels for chemical reactions. A filter membrane is located at the bottom of each well, and beneath the membrane is a waste reservoir. By applying a vacuum, or a reduced pressure, to the waste reservoir, the liquid undergoing test is drawn through the membrane and into the waste reservoir. As the liquid undergoing test is drawn through the membrane, particulates, or the solid phase, of the liquid is deposited on the membrane. The membrane is exposed to the flowing liquid in a limited area, such that the deposited particulates are concentrated. The deposited particulates may be bacteria, cell fragments, or the like.
The membrane may be provided with antigens, haptens, or their antibodies, to react with a target particulate of the liquid to produce a manifestation of a particular combination, the manifestation often taking the form of producing a certain color. Such "chromogenic" assays may be used for simple and quick tests for various bacteria. A small amount, typically no more than one milliliter, of a liquid is dropped into a "well" and caused by a vacuum bias to be drawn through a previously prepared membrane and into a waste reservoir. Particulates in the liquid are retained and concentrated by the membrane and react with the immunoreactant with which the membrane has been previously supplied. Given reactions produce differing colors. For example, a positive indication as to presence in the liquid of a target bacteria may be manifested by a purple color, while a negative indication may be manifested by a white color.
Such devices of the prior art have, on occasion, suffered from "migration" of liquid from one well area to an adjacent well area and, in particular, to a neighboring membrane. U.S. Pat. No. 4,704,255, issued Nov. 3, 1987 in the name of Michael E. Jolley, is illustrative of such devices which typically include a number of wells (96 in the Jolley device), all served by a single membrane and a single waste reservoir. Thus, migration can occur in the membrane itself, and/or in the waste reservoir, from the area of one well to a neighboring well.
It would be beneficial to have available an assay device of the general type above described, but having individual and segregated membrane means for each "well" or test conduit, and individual and segregated waste reservoir means for each of the test conduits.